1. Field of the Invention
The present invention relates to solar energy collection devices, particularly those employing collecting surfaces of a spherical shape.
2. Description of the Prior Art
Solar energy collectors are generally comprised of a flat collecting plate, usually having a top surface blackened or in some other manner made more absorptive of solar energy. A heat transferring medium such as water or air is then brought in contact with the plate either against the top surface or the bottom surface and then removed to a point of utilization. Most commonly, a transparent glass plate is positioned above the blackened flat collecting plate to retain the heat produced by the absorption of the solar energy by the collecting plate.
If the flat plate is retained in a stationary position, such as mounted on the roof or wall of a house, the effective surface area "seen" by the sun changes throughout the day from a thin rectangle early and late in the day to a wider rectangle at midday. Additionally, throughout the year, the north-south movement of the sun's position in the sky changes the angle at which the sun's rays strike a fixed surface. Since the most effective heating is produced by rays which are received perpendicular to the surface of the collecting member, the stationary flat plate devices can present such a perpendicular posture toward the sun only during a very brief portion of the day and then only if the plate is positioned at the proper angle to the sun. This results in uneven energy absorption levels throughout the day and year.
There are devices which overcome a deficiency of the stationary flat plate collectors by employing a tracking clock mechanism which moves the flat plate collector to hold it in a perpendicular position relative to the rays of the sun. The tracking mechanism is an expensive and delicate device which must be calibrated precisely to track the sun throughout the day and provision must be made for changing the angle of the axis of the device to compensate for the north and south movements of the sun through the seasons of the year.
Other solar collectors employ collecting members which may be positioned at a focal point of a parabolic mirror. The mirror is used to concentrate the solar energy on a smaller surface thereby making the collecting member smaller. The same problem of aligning the collecting member or reflecting member with the sun is present in these devices.
Other solar collectors use a cylindrical collecting surface housed in a transparent enclosure to be exposed to the sun throughout the day. This collecting member is filled completely with water which heats up and is drawn off as required for use. However, this type of collector does not provide for proper orientation of the surface of the collector perpendicular to the sun throughout the day and year.